Electrochemical Quartz Crystal Microbalance By: Jay Leitch

What Is E-QCM? History & Background Theory of this technique –Introduction of Basic QCM theory Literature Review –Detection of Antimicrobial drugs Proposal –Combining SERS with EQCM for protein characterization Summary References Outline

What is EQCM? EQCM is an acronym for Electrochemical Quartz Crystal Microbalance It is a extremely sensitive label-free technique that is capable of measuring the mass in the nanogram to sub-monolayer range while simultaneously probing the electrical properties of the system EQCM was first introduced by Kanazawa et. al. in 1990 This technique makes use of the piezoelectric effect of quartz to induce an oscillation at the fundamental frequency (4-10 MHz) of the quartz crystal

What is EQCM Piezoelectric effect: a mechanical deformation (on the order of nm) is produced when an electric field is applied [or vice versa]. W.H. King. Anal. Chem. 1964, 36, This oscillation creates an acoustic shear wave that penetrations into the media above the crystal. This wave is sensitive to changes in the viscosity of the media or physical adsorption of materials onto the crystal, which is typically shown by a decrease in frequency Q. Xie. et. al. J. Chem. Ed. 2007, 84, ~ E ac

What is EQCM? Sauerbrey Equation: (used for perfectly elastic film) where is the change in frequency, is the fundamental frequency of quartz crystal,,, are the area, density and shear modulus of the quartz crystal, respectively, and is the change in mass on the crystal surface

The surface charge can affect adsorption of molecules (i.e. SiO 2 layer carriers negative charge inhibiting adsorption of anionic species) It can be difficult to model since we lack control outside of the sample preparation (solutions cannot be to complicated) Thus, by adding electrochemical techniques, we can alter the charge on the surface to adsorb/desorb a wide range of molecules and we can two independent data sets (i.e. frequency shifts with EC data) to allow for modeling of more complex reactions What is EQCM? Problems with QCM: Solution – Couple with electrochemistry:

What is EQCM?

Counter electrode Adapted from CH instruments Adapted from ALS Adapted from

Uses in Literature Slippage at adsorbate–electrolyte interface (L. Daikhin et. al.) Response of the Electrochemical Quartz Crystal Microbalance for Gold Electrodes in the Double-Layer Region using different electrolytes (V. Tsionsky et. al) Underpotential deposition of metals (Buttry et. al.) Oxide Growth on Ti and Zn (Lemon et. al.) Influence of potential on Immobilized Films (Bott) Swelling and Contraction of Ferrocyanide-Containing Polyelectrolyte Multilayer (Grieshaber et. al.) Monitoring the gold-thiosulfate leaching reaction (Breuer et. Al) Sensor for DNA hybridization (Hwang et. al.)

Literature Review A. Ferancova,J. Labuda and W. Kutner. Electroanalysis. (2001), 13, Electrochemical Quartz Crystal Microbalance Study of Accumulating Properties of the b- Cyclodextrin and carboxymethylated b-Cyclodextrin Polymer Films with Respect to the Azepine and Phenothiazine Type Antidepressive Drugs Goal of the study: Characterize the accumulation properties of antidepressent drugs (shown to the right) in the two polymer films by EQCM. This determining drug accumulation is important in controlled drug release. A. Ferancova, et. al. Electroanalysis. (2001), 13,

Literature Review Experimental Conditions: A. Ferancova, et. al. Electroanalysis. (2001), 13, Pt/quartz (5MHz) electrode - Phosphate buffer (pH 7.4, 0.1M) - levomepromazine (44 μM in cationic state) - accumulation: 120 s at -0.15V -scan rate: 10 mV/s Cyclic voltammograms (1’&1) show a larger anodic peak current for CDPA than CDP The positive shift in frequency (2’&2), which suggests a loss in mass, is smaller for CDPA than CDP. Combining these CV with QCM data suggests the formation stabilized complex between drug and polymer

Literature Review A. Ferancova, et. al. Electroanalysis. (2001), 13, Anodic peak current at 0.8V suggests that the ion exchange is pH dependent (particularly for CDPA) pH 2.5 used to normalize thickness is carboxylates are protonated in CDPA At pH > 3: CDPA becomes deprotonated, which allows for ion exchange of the cationic drug At pH > 7: Deprotonation of drug making it less water-soluble

Literature Review A. Ferancova, et. al. Electroanalysis. (2001), 13, A plateau is obtained for all drugs tested after 120s Current is generally higher for CDPA than CDP Prochlorperazine (III) shows the frequency shift for both polymers, however, trimipramine (V) and chloropromazine (IV) have the highest peak current for CDP & CDPA respectively Conditions: - Conc. of all drugs are 20μM - accumulation V - pH 7.4

Literature Review A. Ferancova, et. al. Electroanalysis. (2001), 13, All signal show an increase with concentration The signals from CDPA are significantly higher than CPD From the concentration data the sorption constant and Gibb free energy sorption can be determined for the various drugs using Langmuir isotherm From the stability constants, the sorption free energy can be determined from:

Conclusions -CDP and -CDPA films are useful for a reversible accumulation of the azepine and phenothiazine type anti-depressive drugs Accumulation is pH dependent with a maximum at pH 7 Drug accumulation is much higher in the anionic form of the -CDPA film than in the non-ionic -CDP film, which makes it more ideal for sensors and drug accumulation and release. The free energy of sorption,, have been determined from the Langmuir sorption isotherms for both polymers.

Proposal a)Monitor changes in the adsorbed bilayer as a function of electrode potential b)Flow water soluble proteins into the EQCM cell and characterize as a function of potential To couple Surface Enhanced Raman with EQCM to monitor the kinetic adsorption of peripheral proteins to a model bilayer and monitor the changes in structure and orientation under the influence of an applied electric field

Proposal Assemble a model cell membrane consisting of DMPC, cholesterol and GM 1 Apply a positive potential adsorption potential (0.4V vs. SCE) Sweep the potential in the negative direction and monitor the change in frequency as the adsorbed layer lifts from the electrode surface Cycle in the anodic direction and record the change in frequency upon re-adsorption of the film This data will confirm whether the desorption -adsorption cycle results in a change in structure of the film or if the bilayer is destroyed upon desorption

Proposal 785 nm Monitor the change in frequency while simultaneously collecting SERS spectra at a constant potential Once the change in frequency reaches a plateau, the maximum coverage is obtained Rinse with electrolyte to remove any unbound proteins Determine the structure and orientation of the adsorbed protein (using SERS) and monitor the change in frequency (QCM) with respect to electrode potential

Summary EQCM is a highly sensitive technique (probe ng –pg) quantities Can simultaneously measure both the physical adsorption processes and electronic properties at the interface Can be used for a wide range of applications such as monitoring mass transport of redox reactions, adsorption/desorption, etc. Can be easily coupled to other spectroscopic techniques

References 1.W.H. King. Anal. Chem. (1964), 36, Q. Xie. et. al. J. Chem. Ed. (2007), 84, H. D. Abruna. Electrochemical Interfaces: Modern Techniques for In-situ Interface Characterization. (1991), p A. Ferancova, et. al. Electroanalysis. (2001), 13, L. Daikhin, et. al. Electrochimica Acta 45 (2000) 3615–21 6.V. Tsionsky, et. al. J. Electrochem. Soc., (1996), 143, D. Buttry and M. Ward. Chem. Rev. (1992), 92, B. Lemon and J. T. Hupp. J. Phys. Chem. B (1997), 101, D. Griershaber, et. al. Langmuir. (2008), 24, D. Gimenez-Romero. J. Electrochem. Soc., (2006), 153, J P. L. Breuer. J. Appl. Electr. (2002), 32, 1167–74 12.Y. Su, et. al. Biotechnol. Prog. (2008), 24,

Langmuir Isotherm